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Realistic STA-2100D

tomcat65

Jun 23, 2018
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I HAVE A REALISTIC STA-2100D VINTAGE STEREO RECEIVER I PICKED UP FOR 100.00.CLEANED UP WELL AND AFTER SETTING BIAS,70MV WAS ON ONE CHANNEL,50MV ON THE OTHER[NO WONDER IT GOT OVEN HOT! SUPPOSED TO BE BETWEEN 8-10MV,EVERYTHING WORKS GREAT EXCEPT THE STEREO LIGHT FOR FM DOESN'T WORK.IT IS NOT BURNED OUT,I CHECKED IT.FM PULLS IN LOTS OF CHANNELS BUT NO STEREO LIGHT.ANY SUGGESTIONS WOULD BE APPRECIATED!
 
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(*steve*)

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ANY SUGGESTIONS WOULD BE APPRECIATED

Turn the volume down so you don't have to shout at us.

I have a realistic sta-2100d vintage stereo receiver i picked up for 100.00.
Cleaned up well and after setting bias, 70mV was on one channel, 50mV on the other (no wonder it got oven hot!) Supposed to be between 8-10mV.

Everything works great except the stereo light for FM doesn't work. It is not burned out, i checked it.

FM pulls in lots of channels but no stereo light. Any suggestions would be appreciated!

That 70mV and 50mV, I presume that was across the output?

Maybe some pictures would help.
 

tomcat65

Jun 23, 2018
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Turn the volume down so you don't have to shout at us.



That 70mV and 50mV, I presume that was across the output?

Maybe some pictures would help.
Measured across resistors on power amp board.pictures of what? The tuner board?
 

(*steve*)

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Measured across resistors on power amp board.pictures of what? The tuner board?

Maybe. I'm not familiar with this device.

Also post links to any service manuals.

Does the receiver produce a stereo signal, or just mono (i.e. is the FM receiver correctly decoding stereo and not displaying the indication, or failing to decode at all)?
 

tomcat65

Jun 23, 2018
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Maybe. I'm not familiar with this device.

Also post links to any service manuals.

Does the receiver produce a stereo signal, or just mono (i.e. is the FM receiver correctly decoding stereo and not displaying the indication, or failing to decode at all)?
I think it may be failing to decode at all,as I am not hearing any difference when I push the mono button in.
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Excellent general photos.

The first thing if check is that the stereo/mono switch results in switching seen on the board. The simplest fault is a faulty switch or broken wires. Whilst these may not be common, they're the easiest to fix.

Detailed photos of the FM board from both sides with all connections labelled would be the next photos of like to see.
 

73's de Edd

Aug 21, 2015
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Sir tomcat65 . . . . .

Here is the power flow path related to the incandescent STEREO indicator lamp of that unit.

Do take note . . . that it is being a small, low power lamp that is only rated at 6V @ 60 milliamperes.
Probably being a very small (grain of wheat) type of lamp construction with leads)

The rest of the lamps are rated at 8V and 300 milliamperes.

HOW IT DO DAT ? . . . . .

12VDC power originates at the bottom left corner at the power supply and is exiting from the emitter of TR705 and routes up via the RED line and feeds one side of " THE " lamp and exits to the right and passes up to the very top and then goes to the left to a 100 ohm voltage dropping / current limiting resistor.
Then it ends at pin 6 of IC204 stereo decoder IC. If a valid stereo signal is being processed, there is an internal driver transistor that effectively "grounds " that line and the STEE_ROW lamp then lights .

TESTING . . . . .

Now you take your DVM and place it in DC CURRENT mode, at a range of greater than 100 milliamperes in preparation.
Then you power up the unit and get a good strong signal with known valid stereo materiel.
We are now considering that the map never lights.
Have one meter lead going to pin IC 6 and take the meters free lead and ground it.
The stereo lamp should now light up, and you immediately want to look at the meters current consumption, and see if it is in the 60'ish or less milliampere range . . . . . OR . . . . . if it is being way above that . . .(some dumb FEWL put the wrong lite bub in it ! )

Standing by for queries . . . . clarifications . . .

RELEVANT SCHEMATIC SNIPPETS . . . . . .

upload_2018-6-24_6-37-40.png

73's de Edd
.....
 
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tomcat65

Jun 23, 2018
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Thanks for the information in the diagram I still have to figure out what I need to connect to as per your instructions as stated tuner brings in stations just not getting any stereo and no light. I have ordered the exact bulb,6 volt,50ma to replace the one that was in there as I broke it trying to get it out thinking it was blown!!So are you saying that you need to use the correct bulb for it to work properly?not say like an 8volt mini bulb?
 

73's de Edd

Aug 21, 2015
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Sir tomcat65 . . . . .

YETH !
. . . . . . all of the power that bulb consumes, has to pass thru a transistor within that IC to ground.

Put a conventional 300ma or 150 ma lamp in its place and you VERY likely will then have the full 120 ma that series 100Ω resistor will let pass, and be taxing the transistor within the IC . . . . possibly popping it.

Another work around alternative . . . yielding an expected half-life span of 1.776893 million years . . . . . is to use a mini RED / YELLOW / GREEN (?) LED in place of the presently utilized mini incandescent lamp.

You confirm the polarity install of the LED leads . . .( GO----- NO GO ) . . . and change the value of the 100 Ω resistor to be about 680-----750 Ω to drop the current consumption on the LED, on down to 20 ma or less.

ASIDE . . . . .
THANK ! goodness . . . . . that we don't have to worry about the main power transformer . . .as it is verified as being a "QUALITY" unit.

Thasssssssit . . . . .

73's de Edd
.....
 
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tomcat65

Jun 23, 2018
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I checked pin 6 on the IC-204 and ground with the other lead on fm stereo station and got 6.3 volts.Light did not come on.
 

tomcat65

Jun 23, 2018
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Something weird going on.measuring off the terminals that are feeding the stereo indicator bulb(dc is measuring 16mv when on a stereo station.Then it will occasionally jump up to 200-300 me then back to 15-16mv. Turning in between stations meter will jump to 7-8 volts. in between channels, dc meter Fluctuates between six and 9 V
 

tomcat65

Jun 23, 2018
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Well I kept fiddling with it I found an 8 V green LED 20 mV fuse lamp and hooked up a temporary connection to the stereo wires that run the stereo light.Someone had turned VR 205 onthe tuner board and it was out of alignment light was flickering all the time and is soon as I turned Vr-205 slightly the stereo light stayed steady tuner was tuned and stereo was back!!! Thank you all for your help and the schematic and information on that little stereo bulb.Sometimes you just keep Diggin And good things happen!!!!cheers to all and thanks for this forum!!!!!!!!!
 

tomcat65

Jun 23, 2018
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Hello again.Solved the fm problem on my Realistic sta-2100D,now there is another problem.Installed new 8 volt bulbs and meter lamps,20ma stereo indicator lamp,turned on the receiver and everything looked great.Heard one click but power button remained red and power transformer was emitting hum. Turned it off and then turned it back on again It still had what I thought was transformer hum and then the line fuse blew.Im puzzled as it was working great prior to the bulb change.Any ideas?Thanks,Tom
 

73's de Edd

Aug 21, 2015
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Sir tomcat65 . . . .

You have Fuse numbers F1 . . .1.5A and F2 . . .2.5A which are related to the supplies of your lighting that you were jes' messin' with.

Fuse numbers 3 . . .1.5A and 4 . . .1.5A are related to regulated power supplies.

Weirdly, the dual, brute strength power supply of the hefty power audio circuitry is not having a fuse.

Give us the assigned number of the blown fuse . . . .

73's de Edd
.....
 

tomcat65

Jun 23, 2018
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in the sta-2100D,the 4 panel 8 volt bulbs are rated at 300ma each.The 4 power meter lamps are rated at 250ma each.By installing led bulbs and fuse lamps only drawing 20ma each,did the power supply not like such a small draw?????Going from a total of 2.2 amps draw to only 160ma total draw??I've changed out vintage pioneer receiver bulbs without any issues.anyone have any thoughts?thanks.
 

73's de Edd

Aug 21, 2015
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That's why I specified the different associations of the 1-2-3-4 fuse positions. If fuse positions 1 and 2 were not the ones blowing, and positions 3 or 4 were, that points to an overload situation with the circuitry of those last two fuse positions. Thus, leaving your 1 and 2 fuse positions not being so suspect.
 

73's de Edd

Aug 21, 2015
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Turned it off and then turned it back on again It still had what I thought was transformer hum and then the line fuse blew.Im puzzled as it was working great prior to the bulb change.

So you still have a unit that plays, but has :
what I thought was transformer hum . . . . . being superimposed in the background.
If so, does running the volume down to absolute zero, decrease that HUMMMM level ?
Or if that doesn't quench the sound can you take an ear and get in close and differentiate if the hum source is coming from the speaker, or from the actual power transformer.
 
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